1. Field of the Invention
The invention relates to photomasks, including a variety of masks and reticles used to form various device patterns in a semiconductor product, a plasma display panel (PDP), a liquid crystal display (LCD) or the like. More particularly, the invention relates to a resist pattern developer, and a method of forming a resist pattern, which are useful for the production of such a photomask, and a product photomask manufactured by use of the developer and method.
2. Description of the Related Art
In the manufacture of semiconductor devices, PDPs, LCDs and the like, various masks and reticles are used for the formation of their device patterns. A mask is a sheet having formed therein an original pattern and positioning marks for positioning the mask during the formation of a desired pattern in an exposure system. A reticle is a mask, which is used in the manufacture of an integrated circuit (IC), having formed therein a pattern for each one IC chip, the pattern being transferred from the reticle to a wafer by a stepper or photo repeater. Although the mask and the reticle are generally called a photomask herein, the following description is mainly directed to a mask, for simplicity.
In the manufacture of a semiconductor device, or a display unit such as PDP or LCD, many steps are carried out to form various patterns, and various masks are used therefor. These masks are made, in general, by forming a light-screening film of, for example, chromium on a transparent substrate of, for example, quartz glass, and patterning the light-screening film by a lithography process (a technique for forming a desired final pattern through formation of a resist pattern by application, exposure, and development of a resist material, etching of an underlying layer by use of the formed resist pattern, and peeling-off of the resist pattern film). For example, as a resist material, an electron beam negative resist suitable for formation of a minute pattern is used, and a portion of a resist film formed of the material to be left as a final mask pattern is exposed, according to given mask pattern data, by an electron beam exposure system, the exposed resist film is then developed using a solvent regarded as a good solvent for the unexposed resist material (a solvent having a higher solubility for the unexposed resist material) to remove the resist material in the unexposed portion which does not form the final resist pattern, and a light-screening film is then patterned by etching using the remaining resist pattern as an etching mask. Thus, in the case where a mask pattern is formed using a negative resist of crosslinking type, a final negative resist pattern for the formation of a mask pattern is formed by crosslinking molecules of the resist material by electron beam irradiation, and transforming the material at the irradiated portion into a condition which is not removed by development.
Electron beam negative resists presently used include resists based on halogenated alkylstyrene, a representative of which is a resist using, as a base resin, a copolymer of chloromethylstyrene and chlorostyrene. In the case of the resist of a copolymer of chloromethylstyrene and chlorostyrene, as a developer therefor, an organic solvent, such as ethyl cellosolve, isoamyl acetate, or methyl isobutyl ketone, is used alone or a liquid mixture of such organic solvents is used.
Recently, mask patterns have been formed at a noticeably higher density and more minutely, and are required to be formed more precisely and to have a higher quality than before.
As a developer used in the formation of a resist pattern prior to the formation of a final mask pattern, a developer, which is regarded as a good solvent for the resist material (resist resin), is used, as referred to above. With a good solvent, absorption of it in a resist resin to be removed for pattern formation is high and, accordingly, the resist resin shows a higher solubility in the solvent.
However, the good absorption of solvent causes occurrence of a phenomenon of swelling of the formed resist pattern. A resin of a negative resist film forms a negative resist pattern in a developing step after exposure since the resin in the exposed areas of the resist film is crosslinked and is therefore not dissolved in a solvent. During the developing step, the resist resin in the indissoluble areas, which forms the resist pattern, absorbs the developer and increases in volume, which is a phenomenon generally called swelling. The resist pattern thus swelled shows deteriorated uniformity of molecular diameter of the resist resin. Consequently, the resultant resist pattern has partially expanded lines, and causes a photomask formed by use of it to have a deteriorated mask pattern and/or deteriorated accuracy in size.
It is thus required that the swelling of a resist during development is inhibited for the formation of a mask pattern required to be formed more precisely and to have higher quality than before.
Accordingly, an object of the invention is to provide a resist pattern developer, and a method of forming a resist pattern, which are capable of inhibiting swelling during development, which is a problem particularly when a resist material based on a halogenated alkylstyrene is used.
Another object of the invention is to provide a photomask, formed by use of the developer and method, having a good configuration of a pattern and excellent accuracy in size.
Thus, in one aspect, the invention provides a resist pattern developer which is a mixture of a solvent regarded as a good solvent and a solvent regarded as a poor solvent for a resist resin based on a halogenated alkylstyrene used for the formation of a resist pattern.
In another aspect, the invention provides a method of forming a resist pattern by forming a film of a resist resin based on a halogenated alkylstyrene to cover a light-screening film previously formed on a substrate, and patterning the resist film by exposure and development to form a resist pattern, the method comprising using, as a developer for the resist pattern to be formed, a mixture of a solvent regarded as a good solvent and a solvent regarded as a poor solvent for the resist resin based on the halogenated alkylstyrene.
In a further aspect, the invention provides a photomask comprising a substrate and a light-screening film having a certain pattern formed thereon, wherein the pattern of the light-screening film is formed by patterning a film of a resist resin based on a halogenated alkylstyrene provided on the light-screening film by use of a developer which is a mixture of a solvent regarded as a good solvent and a solvent regarded as a poor solvent for the resist resin.